The present invention relates to gas-operated, tubular-magazine firearms, such as shotguns, in which an annular piston encircling the magazine reciprocates within a cylinder surrounding a portion of the magazine for actuating the bolt-mechanism when the gun is fired. The invention more particularly relates to means for sealing the piston inwardly with the outer surface of the magazine, as well as outwardly with the walls of the cylinder.
Gas-operated shotguns of the type referred to above have been in commercial use for many years. United States patent to Hillberg U.S. Pat. No. 2,909,101 shows the general arrangement of an annular piston, a magazine tube and a short gas cylinder located at a predetermined distance from the cartridge chamber for handling a wide range of different-powered shot shells in any gauge. One of the difficulties with the Hillberg design is that the annular piston must have a gas-tight fit with the magazine tube on which it slides and therefore requires close manufacturing tolerances in order to maintain concentricity and alignment between the piston and magazine tube over the full distance through which the piston travels with the action of the gun. Any out-of-roundness of the magazine or other deformation results in binding of the annular piston.
One solution to the problems encountered in the Hillberg design is illustrated in the United States patent to Kelly et al U.S. Pat. No. 3,200,710, which shows a gas system similar to that of Hillberg, but with the gas-sealing portion of the annular piston separated from the rest of the piston so that it travels only a short distance toward the receiver after leaving the cylinder, thereby making it necessary to provide a gas-tight fit with the magazine tube only in the short portion that is surrounded by the cylinder. This design is employed in the well-known Remington Model 1100 autoloading shotgun manufactured for many years by Remington Arms Company, Inc. of Bridgeport, Connecticut. As actually produced, however, the two rings that make up the separate gas-sealing portion of the piston are both split, so that as the so-called piston is driven rearwardly against the piston-sealing ring, it wedges this ring outward into sealing engagement with the walls of the gas cylinder and at the same time is itself squeezed inwardly by the mating wedging surfaces into sealing engagement with the magazine tube.
In the United States patent to Beretta U.S. Pat. No. 3,420,140 a short-stroke piston in front of the magazine tube engages a reciprocating sleeve which surrounds the magazine. The principal objection to this arrangement is that the magazine tube must be shortened in order to locate the gas port at the required distance from the cartridge chamber for handling both low and high-power ammunition. Alternatively, if a full-length magazine is used, the gas cylinder must be positioned so far from the cartridge chamber that only high-power shells can be used due to the fact that insufficient energy is imparted to the piston to function the gun properly when low-power shells are fired.
U.S. Pat. Nos. 3,568,564 and 3,657,960 to Badali disclose a short-stroke annular piston around the magazine tube which actuates the breech-bolt mechanism by means of a push-rod attached to a sleeve that slides on the magazine and at the same time telescopes into the annular piston. A split sealing ring interposed between the end of the sleeve and a flange at the front of the piston is provided with a beveled face against which the piston presses when it is driven rearward by the combustion gases in the cylinder, flexing the sealing ring inward into sealing engagement with the magazine tube. Conventional piston sealing rings are employed for sealing the outer surface of the piston with the inner walls of the cylinder.
Means for sealing an annular piston within an annular gas chamber like that employed in the Remington Model 1100 is shown in United States patent to Janson U.S. Pat. No. 3,601,002. In the Janson patent a radially flexible sleeve is loosely attached to the front of the piston so that it can move longitudinally thereof into engagement with an internal sealing ring for wedging the ring into sealing engagement with the magazine, such wedging action causing the sleeve to flex outward into sealing engagement with the walls of the cylinder.
Still another design in which an annular piston is slidably mounted on the tubular magazine of an autoloading shotgun is shown in United States patent to Zanoni U.S. Pat. No. 3,848,511. In this case conventional sealing rings are provided for preventing leakage of gas from the cylinder during the power stroke.
An object of the present invention is to provide satisfactory sealing of the annular piston both inwardly against the magazine tube and outwardly against the walls of the cylinder without the need for providing precise alignment and concentricity of the piston with respect to both the magazine tube and the cylinder. Another object of the invention is to provide a gas-sealing device for an annular piston gas-powered system for autoloading firearms, in which the gas-seals are self-aligning both with respect to the magazine tube on which they are slidably mounted and with respect to the cylinder into which they may be inserted on return of the breech-bolt mechanism to its battery position. Still another object of the invention is to provide such a sealing device which does not employ frictional surfaces that wedge the gas-seals against the magazine tube or against the walls of the cylinder.